Xen 4.4 development update -- RFC for feature freeze timeline

[George Dunlap <George.Dunlap@eu.citrix.com>]

This information will be mirrored on the Xen 4.4 Roadmap wiki page:
 http://wiki.xen.org/wiki/Xen_Roadmap/4.4

= Timeline (RFC!!) =

Here is our current timeline based on a 6-month release:

* Feature freeze: 18 October 2013
* Code freezing point: 8 November 2013
* First RC: 26 November 2013
* Release: 21 January 2014

I've been going through the list and chatting with different
developers, and it seems like there are a number of features in
development that are close to being done, but not quite: they have a
fairly high probability of missing the 18 Oct window, but a pretty
decent chance of making the window if it were extended for a month.

Here are the lists:

Things which will probably make it by 18 Oct:

* Multi-vector MSI (done)
* Improved spice support in libxl (done)
* PVH for domUs
* Non-udev scripts for driver domains
* A raft of fixes from Coverity reports

Additional things which are likely to make it if we extend a month (18
Nov):

* NUMA Memory migration
* Per-vcpu NUMA affinity
* PV NUMA interface
* ARM guest migration
* USB hotplug for libxl

Other things that are a possibility if we slip a month but definitely
not if we stick with the original schedule:

* qemu-xen stubdomains (either Linux or rump kernel / BSD libc)
* Event channel scalability

Obviously there is no guarantee for any of these that a month will
suffice; developers are notoriously bad at estimation and generally
think they can do absolutely anything in 2-3 months.

Nonetheless, it does seem likely that delaying for a month may allow a
significant number of important features to get in.

Any thoughts?

Last updated: 26 September 2016

== Completed  ==

* Multi-vector PCI MSI (Hypervisor side)

* Improved Spice support on libxl
 - Added Spice vdagent support
 - Added Spice clipboard sharing support

== Open ==

* xend still in tree (x)
 - xl list -l on a dom0-only system
 - xl list -l doesn't contain tty console port
 - xl Alternate transport support for migration
 - xl PVSCSI support
 - xl PVUSB support

* qemu-upstream not freeing pirq
 > http://www.gossamer-threads.com/lists/xen/devel/281498
 status: patches posted, tested-and-acked

* Race in PV shutdown between tool detection and shutdown watch
 > http://www.gossamer-threads.com/lists/xen/devel/282467
 > Nothing to do with ACPI
 status: Probably a bug in Linux xen drivers

* credit scheduler doesn't update other fields when tslice updated from sysctl
 > Reported by Luwei Cheng <lwcheng@cs.hku.hk>
 > http://bugs.xenproject.org/xen/bug/16

* Supposed regression from a3513737 ("x86: allow guest to set/clear
 > MSI-X mask bit (try 2)"), as per
 > http://lists.xenproject.org/archives/html/xen-devel/2013-09/msg01589.html.

== Backlog ==

=== Testing coverage ===

* new libxl w/ previous versions of xl
 @IanJ

* Host S3 suspend
 @bguthro, @dariof

* Default [example] XSM policy
 @Stefano to ask Daniel D

* Xen on ARM
 # hardware
  @ianc
   emulator: @stefano to think about it

* Storage driver domains
 @roger

* HVM pci passthrough
 @anthony

* PV pce passthrough
 @konrad (or @george if he gets to it first)

* Network driver domains
 @George

* Nested virt?
 @intel (chased by George)

* Fix SRIOV test (chase intel)
 @ianj

* Fix bisector to e-mail blame-worthy parties
 @ianj

* Fix xl shutdown
  @ianj

* stub domains
  @athony

* performance benchmarks
  @dario

=== Clean-ups ===

* Polish up xenbugtool
  owner: wei.liu2@citrix.com

* ACPI WAET table vs RTC emulation mode
  owner: jan@suse
  prognosis: ?
 > An overly simplified fix was posted a while ago
 > (http://lists.xenproject.org/archives/html/xen-devel/2013-07/msg00122.html),
 > but Tim's objection is rather valid. I can't, however, estimate
 > if/when I would find time to learn what tools side changes are
 > necessary to accommodate a new HVM param, and hence this is
 > currently stalled.  The current solution (as of 3fa7fb8b ["x86/HVM:
 > RTC code must be in line with WAET flags passed by hvmloader"])
 > isn't desirable to be kept for 4.4.

* Sort out better memory / ballooning / dom0 autoballooning thing
 > Don't forget NUMA angle
 - Inaccurate / incomplete info from HV

* Implement Xen hypervisor dmesg log entry timestamps
 > https://xenorg.uservoice.com/forums/172169-xen-development/suggestions/3924048-implement-xen-hypervisor-dmesg-log-entry-timestamp
 > Request seems to be for a shorter stamp (seconds-only, rather than full date)

* Make network driver domains easier to set up / more useful
 - Make it easy to make a device assignable (in discussion)
 - Automatically start/shutdown (xendomains?)
 - Pause booting of other domains until network driver domain is up (necessary?)

* libxl: More fine-grained control over when to pass through a device
 > Some IOMMUs are secure; some are merely functional, some are not present.
 > Allow the adminitrator to set the default

* xl does not handle migrate interruption gracefully
  > If you start a localhost migrate, and press "Ctrl-C" in the middle,
  > you get two hung domains

* libxl / xl does not handle failure of remote qemu gracefully
  > Easiest way to reproduce:
  >  - set "vncunused=0" and do a local migrate
  >  - The "remote" qemu will fail because the vnc port is in use
  > The failure isn't the problem, but everything being stuck afterwards is

* mac address changes on reboot if not specified in config file
  > Needs a robust way to "add" to the config

* qxl
  > http://bugs.xenproject.org/xen/bug/11
  - Uninitialized struct element in qemu
  - Revert 5479961 to re-enable qxl in xl,libxl
  - Option in Xen top-level to enable qxl support in qemu tree
  - Fix sse2 MMIO issue
   - make word size arbitrary

* libxl config file

* libxl: Don't use RAW format for "URL"-based qdisks (e.g., rbd:rbd/foo.img)
  - Figure out whether to use a generic URL or have a specific type for each one
  - Check existence of disk file for all RAW

* acpi-related xenstore entries not propagated on migrate
 > http://www.gossamer-threads.com/lists/xen/devel/282466
 > Only used by hvmloader; only a clean-up, not a bug.

=== Big ticket items ===

* NUMA Memory migration
  owner: dario@citrix
  status: in progress

* Event channel scalability (FIFO event channels)
  owner: david@citrix
  status: RFC v3 posted
  Increase limit on event channels (currently 1024 for 32-bit guests,
  4096 for 64-bit guests)

* PVH mode (w/ Linux)
  owner: mukesh@oracle, george@citrix
  status (Linux): Acked, waiting for ABI to be nailed down
  status (Xen): v12 posted

* ARM stuff: ??

* Meta: PVIO NUMA improvements
 - NUMA affinity for vcpus
    owner: Dario
    status: in progress
 - PV guest NUMA interface
    owner: Elena
    status: v2 posted
 - Sensible dom0 NUMA layout
 - Toolstack pinning backend thread / virq to appropraite d0 vcpu
 - NUMA-aware ballooning
    owner: Li Yechen
    status: in progress

* xl migrate transport improvements
 owner: None
 > See discussion here: http://bugs.xenproject.org/xen/bug/19
 - Option to connect over a plain TCP socket rather than ssh
 - xl-migrate-recieve suitable for running in inetd
 - option for above to redirect log output somewhere useful
 - Documentation for setting up alternate transports

* HVM guest NUMA
  owner: Matt Wilson@amazon
  status: in progress (?)

* qemu-upstream stubdom, Linux
   owner: anthony@citrix
   status: in progress
   prognosis: ?
   qemu-upstream needs a more fully-featured libc than exists in
   mini-os.  Either work on a minimalist linux-based stubdom with
   glibc, or port one of the BSD libcs to minios.

* qemu-upstream stubdom, BSD libc
  prognosis: ?
  owner: ianj@citrix

* Network performance improvements
  owner: wei@citrix

* Disk performance improvements

* Xen EFI feature: Xen can boot from grub.efi
 owner: Daniel Kiper
 status: in progress

* libvirt/libxl integration (external)
 > need a status update
 - owner: jfehlig@suse, dario@citrix

* Default to credit2
 status: Probably not for 4.4
 - cpu pinning
 - NUMA affinity
 - cpu "reservation"

* xenperf
  prognosis: ?
  Owner: Boris Otovsky
  status: v2 patches posted

* blktap3
  owner: thanos@citrix
  status: on hold pending XenServer decision

* Nested virtualization on Intel

* Nested virtualization on AMD

* xl USB pass-through for HVM guests using Qemu USB emulation
  prognosis: Good if extended
  owner: George
  status: v6 patch series posted

* libxl: Spice usbredirection support for upstream qemu
 owner: fabio@M2R
 status: I'll post new patch version shortly

* libxl: usb2 and usb3 controller support for upstream qemu
 owner: fabio@M2R
 status: patch v5 posted, tested and working, awaiting reviews

* Rationalized backend scripts
  owner: roger@citrix
  status: patches posted

* Scripts for driver domains (depends on backend scripts)
  owner: roger@citrix
  status: Patches posted (?)
  prognosis: good

* Multi-vector PCI MSI (upstream Linux)
  owner: konrad@oracle

* xl: passing more defaults in configuration in xl.conf
  owner: ?
  There are a number of options for which it might be useful to pass a
  default in xl.conf.  For example, if we could have a default
  "backend" parameter for vifs, then it would be easy to switch back
  and forth between a backend in a driver domain and a backend in dom0.

* xl PVUSB pass-through for PV guests
* xl PVUSB pass-through for HVM guests
  owner: George
  status: ?
  xm/xend supports PVUSB pass-through to guests with PVUSB drivers
(both PV and HVM guests).
  - port the xm/xend functionality to xl.
  - this PVUSB feature does not require support or emulation from Qemu.
  - upstream the Linux frontend/backend drivers. Current
work-in-progress versions are in Konrad's git tree.
  - James Harper's GPLPV drivers for Windows include PVUSB frontend drivers.

* Guest EFI booting
 - status: tianocore in-tree, some build problems.
   Needs new owner.

* Xen EFI feature: pvops dom0 able to make use of EFI run-time
services (external)
 owner: Daniel Kiper
 status: Just begun

* New kexec implementation
  owner: dvrabel@citrix
  status: v7 posted, only minor updates expected

=== Wishlist / someday ===

* Make storage migration possible
  owner: ?
  status: none
  There needs to be a way, either via command-line or via some hooks,
  that someone can build a "storage migration" feature on top of libxl
  or xl.

* Full-VM snapshotting
  owner: ?
  status: none
  Have a way of coordinating the taking and restoring of VM memory and
  disk snapshots.  This would involve some investigation into the best
  way to accomplish this.

* VM Cloning
  owner: ?
  status: none
  Again, a way of coordinating the memory and disk aspects.  Research
  into the best way to do this would probably go along with the
  snapshotting feature.

* xl vm-{export,import}
  owner: ?
  status: none
  Allow xl to import and export VMs to other formats; particularly
  ovf, perhaps the XenServer format, or more.

* Memory: Replace PoD with paging mechanism
  owner: george@citrix
  status: none

* PV audio (audio for stubdom qemu)
  owner: stefano.panella@citrix
  status: ?

* Wait queues for mm
 > Needed for more advanced paging schemes
  owner: ?
  status: Draft posted Feb 2012; more work to do.

* V4V: Inter-domain communication
  owner (Xen): dominic.curran@citrix.com
  status (Xen): patches submitted
  owner (Linux driver):  stefano.panella@citrix
  status (Linux driver): in progress

* Serial console improvements
  owner: ?
  status: Stalled (see below)
  -xHCI debug port (Needs hardware)
  -Firewire (needs hardware)